The present invention relates to pumps suitable for pumping abrasive and corrosive slurries and the like, and more particularly, to a pump having flexible tubes which are cyclically expanded and contracted to cause the fluid to be pumped.
A flexible tube pump of the general type is shown in U.S. Pat. No. 1,282,145, issued Oct. 22, 1918, to Henri Tobler. Tobler shows a double acting pump comprising a pair of liquid filled cylinders each containing a flexible tube connected to inlet and outlet valves in the cylinders; the cylinders are in communication with opposite ends of a third or control cylinder which contains a piston, the piston being driven by a piston rod extending from one side of the piston and through one end of the control cylinder. Movement of the piston forces liquid alternately into one and out of the other of the pair of pump cylinders to alternately expand and collapse the flexible tubes in alternation to one another whereby to pump fluid continuously from the pump outlet. The Tobler pump suffers the problem of unequal transfer of fluid from the control cylinder to the two pump cylinders, and thus by-pass of liquid around the piston and consequent danger of pump destruction, because of the unequal effective areas of the opposite sides of the piston due to the location of the piston rod on one side only of the piston.
In U.S. Pat. No. 3,609,067, issued Sept. 28, 1971, to Allen C. Wright, a similar pump is shown equipped with a second or balance rod on the opposite side of the piston and extending through the opposite end of the control cylinder, so that the piston areas on both sides are equal and serve to transfer equal volumes of liquid from the control cylinder to each of the two pump cylinders. Theoretically, this should have solved the problem inherent in the Tobler pump.
However, it was soon discovered that the requisite perfect concentricity between the piston rod, the piston, the balance rod and the seals therefor could not be effectively maintained for any prolonged period of time in the service for which the pump was intended. The presence of the balance rod appeared to hasten seal deterioration. Consequently, liquid would by-pass the seal between the piston and the control cylinder, resulting in unequal transfer of fluid from the control cylinder to the two pump cylinders and consequent danger of pump destruction.
Another problem with the flexible tube pumps of the prior art has been failure of the tubes themselves, especially at their seals with the inlet and outlet valves. Both Tobler and Wright (see particularly U.S. Pat. No. 3,489,096, issued Jan. 13, 1970) retained the ends of the flexible tube by ridgedly clamping them between a pair of smooth surfaced, frusto-conical members which were drawn tight against the tube end by threaded fastener means. In such structure, due to manufacturing tolerances and irregularities, the clamping pressure was unequal resulting in concentrated or localized stress in the tube and early stress failure under the repeated expansion and contraction of the tube in use.